1. Technical Field
The present invention relates to a liquid ejecting apparatus having a head unit in which a plurality of heads are sequentially provided in the direction perpendicular to a recording medium transport direction and a controlling method thereof.
2. Related Art
A serial printer such as a dot impact printer, an ink jet printer, and the like functions to print a character or an image by a dot unit or a character unit while moving a print head for ink ejection in the direction perpendicular to a recording medium transport direction. On the other hand, a line printer functions to print a character or an image by a (column) line unit on a recording medium to be transported by a fixed print head.
Among the printers, in the line printer, in order to precisely print an image or a character, it is necessary to increase the number of dots (the number of pixels) per one inch. Accordingly, many nozzles which make it possible to make correspond to the number of dots are provided to the head with a fine distance (for example, see JP-A-2006-15590).
Further, in order to print a color image or the like, the plurality of nozzles are provided on the head so as to separately eject a plurality colors such as cyan, magenta, yellow, black, or the like of ink. Then, by ejecting ink of the each color at a predetermined timing from each nozzle, the ink is applied one from another on a recording medium to be supplied and transported in the recording medium transport direction and an image or a character can be printed.
However, it is difficult to fabricate a head having the fine and many nozzles, and it involves a difficulty to form the head having a length (length in the direction perpendicular to the recording medium transport direction) which allows to print on a recording medium having a size of, for example, A4 size, A3 size, or the like at the same time by one head from the view points of manufacturing technology and cost.
Accordingly, a head unit in which heads each having a plurality of nozzles are sequentially provided in the direction perpendicular to a recording medium transport direction so as to match with the size of the recording medium has been used for the ink ejecting apparatus from the past. In the ink ejecting apparatus, by ejecting an ink drop form the nozzle by driving the head unit based on image information or the like, the ink drop can be landed (applied) on a regular position on the recording medium as a recording medium.
A space is provided between the plurality of heads that are sequentially provided in the direction perpendicular to the recording medium transport direction to constitute the head unit due to various errors of the head shape and size, or attachment. In order to complement the space, one head unit having a length by which an image or the like can be printed along the entire width of a recording medium as a whole is constituted by providing a discrete head in parallel in the recording medium transport direction. By the line head, an ink drop can be applied on a same line on a recording medium.
However, in the conventional line printer, due to the various errors, there is a case in that the head unit itself is attached to incline with respect to a reference direction (for example, the direction perpendicular to the recording medium transport direction) or each head constituting the head unit is attached to incline with each other or with respect to the direction perpendicular to the recording medium transport direction. In this case, the positions of the nozzles provided in each head also incline (positionally shift) in a similar way. As a result, ink is landed at a position shifted from a regular position of the recording medium supplied and transported in the recording medium transport direction. As a result, color shift due to color mixture failure or banding (strip shaped print unevenness generated in the direction perpendicular to the recording medium transport direction) generates in a print image.